The present invention relates to a method and a device for controlling the clutch of a vehicle.
As is known, during the operation of opening and closing of the clutch, for example during gear-changing or acceleration manoeuvres of the vehicle, the torque value transmitted by the engine to the drive wheels via the clutch itself depends mainly on the load acting on the clutch disc, the value of which depends on the position of the actuating lever of the clutch itself.
The clutch actuating operations are normally performed manually by the driver of the vehicle, who adjusts the approach position of the clutch so as to obtain a substantially gradual transfer of the torque through the clutch itself and therefore a comfortable travel progression of the vehicle.
It is also known to perform the clutch actuating operations in an entirely automatic manner by means of electronic control devices which have the purpose of adjusting, during operation of the clutch, the position of the actuating lever of the clutch itself depending on a plurality of input signals.
An example of embodiment of a control device of the electronic type is shown in FIG. 1.
According to that shown in this figure, the control device, denoted in its entirety by 1, operates, by means of an actuator 2 driven by a solenoid valve 3, an actuating lever 4 (of the known type and shown schematically) of a clutch 5 arranged between the output shaft 6a of an engine 6 (shown schematically) and an input shaft 7a of a gearbox 7 (shown schematically).
In particular, by means of the actuating lever 4 it is possible to vary in a known manner the load acting on a disc (not shown) of the clutch 5 and therefore the torque transmitted through the clutch 5 itself.
The control device 1 comprises a signal generator circuit 8 receiving at its input a plurality of information signals S.sub.INF and generating at its output, on the basis of the input signals, a reference torque signal C.sub.RIF, the instantaneous value of which indicates the desired value of the torque transmitted via the clutch 5.
In particular, the information signals S.sub.INF on the basis of which the reference torque signal C.sub.RIF is generated, are signals correlated to parameters of an operational nature and relating to the status of the vehicle, namely parameters such as, for example, the position of the accelerator pedal, the angular velocity of the engine 6, the angular velocity of the clutch 5, the position of the brake pedal, etc.
The control device 1 comprises, moreover, an adder circuit 9 receiving at its input the reference torque signal C.sub.RIF and an estimated torque signal C.sub.ST, the instantaneous value of which indicates the estimated value of the torque transmitted through the clutch 5, and generating at its output an error signal C.sub.E resulting from the difference between the reference torque signal C.sub.RIF and the estimated torque signal C.sub.ST.
The control device 1 comprises, moreover, a control circuit 10 of the known type, for example of the proportional-integral type PI, receiving at its input the error signal C.sub.E and generating at its output a control signal C.sub.M used for operating the solenoid valve 3 and therefore for controlling the actuator 2 and adjusting the position of the actuating lever 4.
The control device 1 comprises, moreover, a position sensor 11 coupled to the actuator 2 and generating at its output a reaction signal X correlated to the operational position of the actuator 2 (and hence to the position of the actuating lever 4 of the clutch 5) and a memory 12 receiving at its input the reaction signal X and generating at its output the aforementioned estimated torque signal C.sub.ST.
In particular, the memory 12 has stored in it a table containing a plurality of numerical values defining a transmissibility function F(X) of the clutch 5, which enables a corresponding value of the torque transmitted through the clutch 5 itself to be estimated for each of the positions assumed by the actuating lever 4 of the clutch 5.
In detail, the transmissibility function F(X) of the clutch 5 defines a one-to-one association between each of the instantaneous values x.sub.i of the incoming reaction signal X and a corresponding instantaneous value, indicated by C.sub.FRIZ.sbsb.--.sub.OLD, of the outgoing estimated torque signal C.sub.ST ; therefore a plurality of pairs of values are stored in the memory 12, each pair relates to a respective position assumed by the actuating lever 4 and comprises an instantaneous value x.sub.i of the reaction signal X and a corresponding instantaneous value C.sub.FRIZ.sbsb.--.sub.OLD of the estimated torque signal C.sub.ST.
During use, the control device 1 operates in the form of a closed loop following the reference torque signal C.sub.RIF generated by the signal generator circuit 8 and operating, via the solenoid valve 3, the actuator 2 of the actuating lever 4 of the clutch 5. In particular, on the basis of the position of the actuator 2, the memory 12 generates at its output the estimated torque signal C.sub.ST supplied to the adder circuit 9 so that the torque transmitted to the drive wheels of the vehicle is as far as possible equal to the desired torque, in order to obtain a substantially gradual transfer of the torque through the clutch 5 and therefore a comfortable travel progression of the vehicle.
The progression, over time, of the torque transmitted through the clutch 5 during operation of the clutch 5 itself depends substantially on the progression of the aforementioned transmissibility function F(X), which is in turn dependent upon the mechanical characteristics of the clutch 5.
The mechanical characteristics of the clutch 5, however, are subject to changes during the life of the clutch 5 itself on account of inevitable phenomena of wear and variations in the operating temperature of the clutch 5.
Therefore, when the transmissibility function F(X) no longer reflects the actual mechanical characteristics of the clutch 5, electronic control of the torque transmitted through the clutch 5 becomes unreliable and therefore results in a worsening in the performance of the vehicle during the gear-changing and acceleration manoeuvres.